Field of the Invention
The present invention relates to a photoelectric conversion device and a method of manufacturing the photoelectric conversion device.
Description of the Related Art
In a photoelectric conversion device for detecting light information by a photoelectric conversion element, it is important to suppress a dark current which flows into the photoelectric conversion element in order to reduce a noise component which is superimposed to signal charges.
Japanese Patent Application Laid-Open No. 2002-217397 proposes a method whereby in order to reduce a dark current which flows into a photodiode as a photoelectric conversion element, a negative voltage is applied to a gate electrode of a transfer transistor during a charge accumulation period in the photoelectric conversion element. According to such the method, since a channel of hole is formed in an interface between an oxide film and a semiconductor substrate under the gate electrode of the transfer transistor serving as a source of the dark current, the generation of the dark current can be suppressed. On the other hand, according to the method disclosed in Japanese Patent Application Laid-Open No. 2002-217397, since a potential difference between the gate electrode of the transfer transistor and a floating diffusion region is large, there is a risk that in association with a deterioration in a gate insulating film of the transfer transistor, a reliability to insulating performance of the relevant portion decreases remarkably.
Japanese Patent No. 5016941 proposes a method whereby a negative voltage is applied to a gate electrode of a transfer transistor during a charge accumulation period in a photoelectric conversion element and a voltage of a floating diffusion region is set to a value lower than a power supply voltage. According to this method, since an electric field which is applied between the gate electrode of the transfer transistor and the floating diffusion region is reduced during the charge accumulation period, a deterioration in a gate insulating film in the relevant portion can be suppressed.
However, according to the method disclosed in Japanese Patent No. 5016941, by setting the voltage of the floating diffusion region to the value lower than the power supply voltage, a ratio at which charges overflowed from a photodiode during the charge accumulation period leak into an adjacent pixel is larger than a ratio at which such charges are moved to the floating diffusion region. Thus, there is a case where leakage characteristics into the adjacent pixel deteriorate.